In unitary electric-motor/hydraulic-pump assemblies, the pump portion of the assembly is mounted on one end of the housing of the electric motor and coupled to the motor shaft within the assembly. During operation of the pump, reaction forces generated by the pumping members are transmitted to the pump support structure and through the bearings to the pump shaft. This vibration energy is therefore transmitted both directly to the motor housing, and through the shaft to the motor components and thence to the motor housing, which provides a large surface for radiating energy into the surrounding atmosphere as audible noise. Furthermore, noise is generated by vibration through the motor housing mounting feet to the support structure on which the motor/pump assembly is mounted.
Noise radiation in industrial environments is of increasing concern from the standpoint of health and safety of equipment operators. It has heretofore been proposed to place isolation pads between the motor mounting feet and the underlying support structure to inhibit transmission of vibration noise to the support structure. See "Noise Control in Hydraulic Systems" published by applicant's assignee in 1991, Publication No. 510-H91GG. When a load is applied to the motor, the reaction torque is supported by one set of isolation pads, and the opposite set is unloaded. If the isolation pads on the unloaded side do not include material between the motor foot and the tie-down bolts, the vibration noise will be transmitted directly to the support structure. Moreover, such isolation pads have no substantial effect on radiation of noise from the motor housing.
It is a general object of the present invention to provide a unitary electric-motor/hydraulic pump assembly of the described character that includes facility for suppression of noise radiated into the atmosphere from the motor/pump housing, and/or suppression of vibration transmitted directly from the motor housing to the underlying pump/motor assembly support structure.